The present invention relates to vehicle speed measurement apparatus. Radar-type vehicle speed measurement have been used for many years. However, they are easily detected by vehicle carried radar detectors and have numerous problems regarding accuracy, reliability and operator safety. Pairs of spaced roadway tubes have been used to measure speed of vehicles, but these require substantial spacing between tubes, and any stretching of the tubes induces inaccuracies in speed measurements. Moreover, if the first tube is spotted by a speeding driver, a quick braking action between the spaced tubes can enable the driver to possibly avoid detection.
According to the present invention, a pair of closely spaced (within a few inches or less) piezoelectric sensors of the same length are encased in a common rubber extrusion so that they are parallel to one another and at a predetermined distance apart, which is maintained by the rubber extrusion. The device is placed in a lane and is large enough to sense the speed of each vehicle traveling in that lane. It has a low profile to the road surface and can be camouflaged to deter visual detection. A linear weight, such as a flat strip of heavy metal such as lead, is encased under the rubber extrusion to keep it immobile while vehicles are traveling over it. The spaced piezoelectric sensors are coupled to a time measuring circuit to measure the peak times of voltage pulses induced in the closely spaced piezoelectric sensors. The measuring circuit, which may include a microprocessor, calculates the vehicle's speed and displays it on a portable monitor. The system is self-testing to insure accuracy prior to operation. The system can be powered by batteries or from a remote cigarette lighter adaptor. The system allows the operator to monitor the speed of each vehicle that travels over the speed sensor or freeze the speed of the last vehicle. The system could be modified to perform volume and speed recordings.